1. Field of the Invention
The present invention relates to an obstruction detecting method for use in a power window apparatus and a power window apparatus. More particularly the invention relates to an obstruction detecting method for use in a power window apparatus and a power window apparatus, capable of preventing an excessive pinching force from acting on an object pinched or caught in a power window, even in a case of cessation of a supply of two phase pulses (a two-phase pulse signal) from a pulse generating section coupled to a window opening and closing motor.
2. Description of the Related Art
Among power window apparatus which have been previously employed for opening and closing a window of a motor vehicle, there has been known a power window apparatus which detects the pinching of an object in the window, and for stopping or reversing the window opening and closing motor at the detection thereof.
In this type, a conventional power window apparatus is made up of, at a minimum, a motor for opening and closing a window, a motor driving section for driving the motor rotationally, a pulse generator for generating a pulse in the rotation of the motor, a micro control unit (MCU) for controlling the entire operation of the apparatus, and operating switches for opening/closing the window manually.
In the aforesaid conventional power window apparatus made to detect the obstruction, in response to an operation of any one of the operating switches, the micro control unit supplies a drive signal through the motor driving section to the motor to rotate the motor in the forward direction or in the reverse direction in accordance with the switch operation so that the window is driven in the opening direction or in the closing direction. On the rotation of the motor, the pulse generator coupled to the motor operates to output a pulse signal comprising pulses. At this time, the micro control unit calculates the interval between the edges of the pulse signal outputted from the pulse generator by counting a clock signal to obtain a motor torque value on the basis of the calculated pulse edge interval. This is used for comparing the obtained motor torque value with a reference median stored previously in its internal memory. If the motor torque value exceeds the reference median by a substantial amount, the micro control unit makes a decision that a pinching in the window has occurred, and immediately stops or reverses the rotation thereof.
Thus, the conventional power window apparatus and obstruction detection apparatus is designed such that the motor torque value is obtained on the basis of the pulse edge interval of two phase pulses outputted from the pulse generator to compare the motor torque value with a reference median, thereby making a decision on the occurrence/no occurrence of the pinching in the window.
However, the aforesaid power window apparatus creates the following problem. That is, since the decision on occurrence/no occurrence of the pinching therein is made after the detection of the pulse edges of pulses outputted from the pulse generator, in the case in which the motor is locked abruptly because a high-rigidity object is pinched in the window, the micro control unit cannot detect the pulse edges of the output pulses of the pulse generator so that difficulty is encountered in obtaining the pulse edge interval in the micro control unit, which leads to the difficulty of obtaining the motor torque value on the basis of the pulse edge interval. This causes a pinching force exceeding a reference value (a value calculated by adding a preset reference allowable value to the reference median) to act on the object pinched.
In addition, in the case of the aforesaid power window apparatus, there arises problem if there is no output of a pulse signal from the pulse generator or no transmission of the pulse signal to the micro control unit. For example, if a magnetic sensor built in the pulse generator gets out of order, if a cable for leading the pulse from the magnetic sensor to the micro control unit breaks down, or if a breakage or a contact failure of a cable connector installed on the pulse generator side or on the micro control unit side occurs. If the pulse signal outputted from the pulse generator does not reach the micro control unit at all, difficulty is experienced in calculating the pulse edge interval in the micro control unit so that the motor torque value is unobtainable on the basis of the pulse edge interval. Hence, if the pinching into the window occurs during this time, the detection thereof becomes impossible. Still additionally, in the case in which the pulse generator generates two phase pulses, if only the one phase pulse of the two phase pulses does not reach the micro control unit, although the micro control unit can obtain the pulse edge interval, the obtained pulse edge interval doubles approximately to the intended pulse edge interval and, accordingly, the motor torque value based on the pulse edge interval also doubles approximately so that, irrespective of no occurrence of the pinching into the window, a false detection representative of the occurrence pinching therein takes place.